I'm not sure what risk you think there is in putting in a promo code? How do you think using a promo code could be used against you?
All a promo code does is tell the checkout system to apply a specific discount to your order. It might have some requirements like Nano X added to order to receive 50% off Nano S... or it might be "set shipping to $0 if 2x Nano S added to order" etc...
Using a promo code is not going to infect your PC with malware or reveal your seed or mean you get sent a modified ledger...
At worst, it might "link" your purchase to someone providing an affiliate code, but they're not the same as promo codes... affiliate codes don't tend to provide a discount.
And given affiliate codes tend to get posted all over the place, being linked to an affiliate doesn't really much to anyone... except perhaps the person who owns the affiliate code... and they don't even get details of your purchase, they just get some $